Conventionally, a structure is known in which a yoke at the axis end portion of a propeller shaft of a vehicle is connected to a flexible coupling (see Patent Literature 1, for example). With such a connecting structure of the propeller shaft, it is possible to transmit rotation torque by elastically connecting the propeller shaft and to absorb vibration and flexure by the flexible coupling.
The yoke of the propeller shaft disclosed in Patent Literature 1 includes three arm portions, each extending outward in the radial direction. The three arm portions are disposed at an interval of 120° in the circumferential direction. The arm portions of the yoke of the propeller shaft are connected on both sides of the flexible coupling with bolts and nuts, with the position of each arm portion being shifted by 60° from the opposing position thereof.
In addition to the propeller shaft described above, a propeller shaft is conventionally known that includes a yoke having four arm portions disposed at equal intervals in the circumferential direction.
FIG. 11 is a schematic view showing an example of a propeller shaft 50 that includes, at an axis end portion thereof, a yoke 60 in which four arm portions 61 to 64 are provided at equal intervals in the circumferential direction. Each of the four arm portions 61 to 64 extends outward in the radial direction, and has the same shape.